"What is the book that changed your life? (not novels or religious texts)"
I think it's a wonderful way to connect in a less superficial way and learn a little more about each other. It's also a wonderful way to discover new books worth reading.
This is one of them:
Using Your Brain: For a Change
NLP offers a conceptual understanding that is solidly based on information science and computer programming, yet rooted even more thoroughly in the observation of living human experience. Everything in NLP can be directly verified in your own experience, or by observing others. The new submobility patterns described and taught in this book are even faster and more powerful ways of creating personal change than the earlier NLP methods.